Tag Archives: Ganoderma adspersum

California Pest Rating for

Ganoderma adspersum (Schulzer) Donk

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

On January 25, 2017, Dr. David Rizzo, Professor, Department of Plant Pathology, University of California, Davis, notified CDFA of his detection of Ganoderma adspersum in almond orchards in the San Joaquin Valley, during surveys which initiated during fall 2015, of almond trees for wood decay fungi. The fungus was noted to be very aggressive and had killed relatively young almond trees in some orchards. Consequently, CDFA will collect official samples of the fungus for analysis at the CDFA Plant Pathology Laboratory, and for official record. Ganoderma adspersum has not been reported earlier from California or North America (Rizzo, 2017a). The potential risk of infestation of G. adspersum is assessed here and a permanent rating is proposed for the species.

History & Status:

Background: Ganoderma adspersum is a wood-decaying fungus that occurs in a very wide range of tree species including deciduous trees and conifers throughout the world. The species has more frequently been detected in trees growing near human habitations, gardens, parks, and planted sites (Papp & Szabo, 2013; De Simone & Annesi, 2012). Ganoderma adspersum is a pathogen of roots and butts of living trees causing white rot, and can continue to grow saprophytically on nonliving tissue such as, stumps of felled trees (De Simone & Annesi, 2012). Ganoderma species often kill their hosts and frequently, a diseased tree breaks or is wind-thrown while still alive as a result of decay in the butt and base of the trunk (Sinclair & Lyon, 2005). Unlike other closely related species, G. adspersum is an aggressive species that is able to penetrate and break through intact reaction zones of infected wood causing progressive and extensive decay over a relatively short period of time (De Simone & Annesi, 2012). In Italy, G. adspersum-infected pine stands were felled within two years of infection (De Simone & Annesi, 2012).

Ganoderma adspersum has been known by several names. The fungus was originally found growing on Carpinus betulus (European hornbeam) in Croatia, and published by Schulzer 1878 as Polyporus adspersus, and later as P. linhartii Kalchbr. 1884, Ganoderma linhartii (Kalchbr.) Z. Igmándy 1968, and G. europaeum Steyaert 1961. After studying all specimens under the different species names, in 1969, Donk concluded the correct name for the fungus, G. adspersum (Tortic, 1971). In European polypore monographs, G. adspersum was found under the name, G. australe (Fr.) Pat. 1889. However, through molecular analysis, the European taxon (G. adspersum) was differentiated from the Australian taxon (G. australe). Ganoderma adspersum is the name of the European species (Papp & Szabó, 2013). Differentiation of species of Ganoderma is confusing and problematic with only seven species, including G. adspersum, being accepted in the European polypore monographs (Papp & Szabó, 2013). Taxonomically, G. adspersum is a distinct species belonging to the G. applanatum – australe complex (Papp & Szabó, 2013).

The species was first reported from Europe and is primarily found in that continent. However, it has also been found in Argentina, Brazil, American Samoa, and recently in the USA (California) (see: ‘Worldwide Distribution’).

In California, Ganoderma adspersum was detected in nine and ten year old almond orchards trees in Kings County during surveys of almonds for wood decay fungi in February 2016 (Rizzo, 2017a) Over a three-year period, the orchard had experienced almost 20% tree loss, resulting in its removal by the end of 2016. This detection marked a first for the fungus in California and North America. Another detection was made in August 2016, in a twelve-year old almond orchard in Fresno County, and in 2017, additional infections were detected in Tulare, Kern, and Madera Counties (Rizzo, 2017b). Presently, in California, the fungus has been found only in almond, prune and peach. All surveyed almond trees were planted on peach rootstock (Rizzo, 2017b).

Disease development: Generally, most infections are initiated by airborne basidiospores that enter wounds on roots and trunk bases. Basidiocarps (fruiting bodies or conks containing numerous spore producing structures or basidia) usually grow from the vicinity of old wounds. Basidiospores are produced in great numbers during evening hours when the air is humid. Experimentally, infection by root contact with previously colonized wood is also possible, although tree-to-tree spread has not been indicated by field observations (Sinclair & Lyon, 2005).

Symptoms: In general, trees affected by Ganoderma develop widespread decay of sapwood in the butt and major roots. Other symptoms include loss of vigor, undersized and sometimes yellowing or wilting leaves, thin crowns, and dead branches. Some infected trees may die while others are weakened and fall by windstorms as a result of decay. In advanced stages of decay, wood is light colored and stringy or spongy. Large, reddish brown basidiocarps of G. adspersum grow from roots or butts (Sinclair & Lyon, 2005). Progression of decay may be favored by predisposing conditions such as wounds, excessive stem density, or water stress (De Simone & Annesi, 2012).

Damage Potential: Ganoderma adspersum causes wood decay and root rot thereby decreasing structural strength, growth and stand of infected trees. In California, Rizzo (2017b) reported 50% to 70% infection rates in almond and prune orchards, with tree loss being exponential over time. Very high infection levels were observed in 9-12 years old almond orchards. The life span of a typical almond orchard is about 25 years. However, extensive infections may be terminal for almond orchards. Few orchards were removed entirely due to high infections of Ganoderma adspersum.

Official Control: No official controls are reported for Ganoderma adspersum. However, Ganoderma spp. is on the “Harmful Organism Lists” for Colombia and Jamaica. Shipments of Ganoderma spp.-free Phoenix dactylifera, (date palm) plants is required by Colombia (USDA PCIT, 2017).

California Distribution:Ganoderma adspersum has been found in almond and prune orchards in Fresno, Kings, Tulare, Kern, and Madera Counties (Rizzo, 2017b).

California Interceptions: None reported.

The risk Ganoderma adspersum would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Presently, Ganoderma adspersum has been found in almond and prune orchards within the San Joaquin Valley. It has therefore demonstrated its capability to establish under suitable climates for those hosts within the State.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 3

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range:Ganoderma adspersum has a wide host range which includes deciduous and confer trees reported worldwide. However, in California, the fungus has presently been detected in almond, prune and peach (almond on peach root stock) (Rizzo, 2017b). Those fruit hosts are cultivated in significant acreage in California.

Evaluate the host range of the pest.

Score: 3

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Numerous basidiospores are produced by the fungus but are dependent on wind currents for dispersal and spread to non-infected trees. Therefore, a Medium rating is given for high reproductive potential.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 2

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Rizzo (2017b) reported 50% to 70% infection rates in almond and prune orchards in California, with tree loss being exponential over time. Ganoderma adspersum causes wood decay and root rot resulting in decreased structural strength, growth and stand of infected trees. Few orchards were removed entirely due to high infections.

Evaluate the economic impact of the pest to California using the criteria below.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: Ganoderma adspersum has been reported on several hosts that are found in California environments. Internationally, the fungus has more frequently been detected in trees growing near human habitations, gardens, parks, and planted sites. However, in California, the fungus has only been detected in cultivated almond and prune. Other hosts may be threatened if the almond isolate in California is able to infect them. However, as presently this is not known, the fungus is given a Medium score for potentially impacting urban gardens and plantings.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

Consequences of Introduction to California for Ganoderma adspersum:High(13).

Add up the total score and include it here.

-Low = 5-8 points

-Medium = 9-12 points

–High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Uncertainty:

Presently, in California, Ganoderma adspersum has only been found in almond, prune, and almond on peach rootstock. The fungus has a wide host range, but it is not known if other hosts, in particular those in natural environments of California, have been infected or will be infected by the almond isolate of the fungus. Future information on its distribution may alter the numerical score but less likely, the proposed rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Ganoderma adspersum is B.